In the blood pressure measurement with the oscillometric method, the compressing pressure, that is, the cuff pressure of the cuff wrapped around a predetermined site (e.g., upper arm) of the living body is gradually changed in speed to extract the vibration component generated at the cuff in the process, that is, the amplitude of the cuff pulse wave (pressure pulse wave). The blood pressure is calculated based on the change of the extracted pulse wave amplitude with respect to the cuff pressure.
In a general electronic sphygmomanometer of the oscillometric method, pressure control as well as pulse wave signal analysis, blood pressure calculation, and blood pressure display are automatically carried out. While the cuff pulse wave is being measured, the pulse wave information not preferable in the calculation of the blood pressure sometimes get mixed as noise due to the movement (body motion) of the body, the vibration of the outer environment, and the physiological state such as irregular heart beat.
In the conventional electronic sphygmomanometer, devisal is made such as removing or correcting the unnecessary pulse wave information with a unique algorithm. However, when automatically detecting noise and automatically correcting the pulse wave amplitude, the noise may not be completely removed and may become an error, or an appropriate correction may not necessarily be performed. Furthermore, whether or not the noise is really removed cannot be recognized since the correction algorithm of the pulse wave amplitude is unknown to the user.
Patent document 1 (Japanese Unexamined Patent Publication No. 07-236617) proposes easily determining the appropriateness of the measurement state by displaying information on the corrected (smoothed) pulse wave amplitude. Patent document 2 (Japanese Unexamined Patent Publication No. 2002-272689) proposes making the determination on whether or not the reliable blood pressure value is obtained during the blood pressure measurement by displaying the normalized pulse wave amplitude in a graph during the blood pressure measurement.
Patent Document 1: Japanese Unexamined Patent Publication No. 07-236617
Patent Document 2: Japanese Unexamined Patent Publication No. 2002-272689